A common design for built in camshafts in internal combustion engines is to allow the camshaft to rest on fixed bearings, either in the engine block or in the cylinder head. When the camshaft is assembled into the engine it is inserted through the fixed camshafts bearings, which have the same diameter as the camshaft bearing journals. This is foremost a very common design on engines with a push rod valve train, but can be found on other types of valve trains, for instance side valve engines.
Designs following the guidelines as mentioned above will result in limitations on how the camshafts lobes on the camshaft can be designed when located close to the camshaft bearing journals. The largest radius on the camshaft lobe cannot be allowed to be larger than the radius of the camshaft bearing journal, since it then would be impossible to insert the camshaft through the camshaft bearings.
By designing the camshaft bearing journals as detachable details assembled on the camshaft at the same time or after the camshaft is assembled into the engine, it becomes possible to radially displace the camshaft during assembly into the engine, which hence makes it possible to design camshaft lobes with a larger radius than the camshaft bearing journals.
There are earlier examples of camshafts designed in several separate sections. In DE 2706021 A1, aimed at large internal combustion engines where it, for handling and assembly reasons, is an advantage to split the camshaft in several smaller parts. To be able to apply this type of design on smaller engines with corresponding smaller camshafts, new solutions for assembling the parts of the camshaft together are needed, otherwise these details will strongly limit the earlier described advantages.
In U.S. Pat. No. 2,552,754A another divided camshaft design is described. This is however a design that still limits the design of the camshaft lobes according to the camshaft bearing journals. Hence this design does not solve the problem referred to herein.
When designing a completely new engine with the purpose of a simple and low cost solution, a design with fixed camshaft bearings is very attractive. The dimensions of the camshaft bearings are then adapted after the intended design of the camshaft lobes. A design with detachable camshaft bearing journals would then most likely be counter-productive since it complicates the design and makes it all but simple. If the designer would need larger camshaft lobes he would instead make the camshaft bearings larger, or choose a design with detachable camshaft bearing caps, which means the camshaft does not have to be inserted through the camshaft bearings during assembly, and the problem is avoided.
This invention is therefore best suited when the radius of the camshaft lobes needs to be increased on an existing engine, usually for performance reasons. The skilled professional presented with this problem today solves it by modifying the engine by increasing the camshaft bearings and correspondingly increasing the camshaft bearing journals. This solution is limited by the available space in the existing design and complicates other qualities of the engine. Another solution used is to machine an axial notch in the camshaft bearings, where the tip of the camshaft lobes can be inserted. This design also has a negative impact on other engine properties.
These are solutions that allow for only minor increase of the radius of the camshaft lobes that, in addition, require modification to camshaft bearings and other parts.
The invention distinguishes itself from the described designs of divided camshafts by the fact that it has to be assembled together at the same time it is inserted into the engine. Thus, one must already, when designing the camshaft, have in mind in which order the parts should be assembled, to take advantage of the design. The main purpose of the earlier designs has been to divide large camshafts into smaller and more manageable details to ease manufacturing and assembly into the engine.
The main purpose of this invention is to enable camshaft lobes with a larger radius than the radius of the camshaft bearing journals to be designed. To achieve this purpose in the best way, it demands the details of the design to differ from already available solutions.